Interfering rattling noises occur in a boat transmission particularly when the boat travels forward or backward during a low idling speed of the motor. The reason for these rattling noises are torsional vibrations of the motor on the one hand and low propeller torques on the other hand. Because of the reduced distorting of the gears, a chattering of the tooth flanks takes place. Such torsional vibrations are in addition enhanced by the fact that, due to engine-specific viewpoints, the inertia moment of the flywheel is more and more reduced. To reduce such torsional vibrations, torsion shock absorbers are utilized.
However, there are cases in practice in which common torsion shock absorbers are not sufficient in curing the problem of torsional vibrations. The reasons for this are among others:
the path of rotation is too small, in particular in the first step; PA1 hard transition between the individual attenuation steps.
Furthermore two masses--flywheels with hydraulically damped vibration cancellation means--are known, which, however, are complicated and are too expensive for the here existing use.
In a torsion shock absorber of the above-mentioned type, which shock absorber is described in DE-34 90 360 C2 (corresponds to U.S. Pat. No. 4,650,053), the elastic elements formed by the helical springs act in tangential direction and the associated support surfaces of the primary part and of the secondary part are at a right angle with respect to the longitudinal axis of the helical springs. The relative rotation of the primary and secondary part is in such a torsion attenuator only small and is limited by the number and the length of the helical springs. The helical springs can only be compressed until their coils rest on one another. The possible relative rotation could only be increased by a correspondingly greater length of the helical springs which, however, is only possible to a limited degree.